Food-stuffs are susceptible to a wide variety of microbial infestations. These are rarely beneficial and frequently harmful. Those of a harmful nature can cause mild tainting of the food-stuff, or illness ranging from mild stomach ache to death in the consumer, always assuming that the food is not rendered completely inedible.
Very few forms of infestation are likely to lead to death, but one well known example is Salmonella infection of canned products. Other harmful infestations are generally of a less serious nature but, nevertheless, spoil the product. An example of this kind is Clostridium infection, which can affect both human and animal feeds. Milk products are particularly prone to infection, especially cheese, and the result is an unpleasant acid taste combined with uncotrolled gas production, which may also cause an unsightly, deformed product.
In other areas, microbial infestation need not always be undesirable. Production of certain cheeses, for example, is totally reliant on the presence of certain fungi, and yoghurt is a thick culture of harmless bacteria.
Bacterial cultures are also of use in their own right and are becoming increasingly important with recent break-throughs in biotechnology. However, such cultures become useless if contaminated by virus (bacteriophage, or phage).
Phages were first recognised in the early 1960's. Since then, attention has been focussed on them for two reasons; their effect on the bacterial cell and their ability, in some instances, to translocate bacterial genes. This latter ability is particularly important to present day genetic studies and has enabled the development of useful gene cloning techniques. Phages are, nevertheless, being superseded by other systems less likely to damage the organisms concerned. Cultures infected by uncontrolled phage are useless, as no means are available to combat virus infection. Such cultures can only be destroyed.